The invention relates generally to wrenches for opening and closing valves operable by hand wheels and more particularly to a power valve wrench having a motor which drives a hand wheel engaging member through a speed reduction device.
In refineries, petrochemical plants, steam or nuclear power generating plants, water treatment plants and other facilities where large liquid and gas flows are common, significant numbers of large valves are equally common. Typically, such valves are operated by hand wheels having diameters of from several inches to a few feet. Although hand wheel size is related generally to the size of the valve and the torque necessary to open and close it, the actual torque necessary to open and close a valve, either as it ages or is only occasionally operated, can increase dramatically from the initial operating torque. In many instances, the operating torque of an aging or seldom used valve may be great enough to present the potential for human injury or it may simply render it inoperable.
This problem has been addressed in the prior art. For example, U.S. Pat. No. 1,460,922 discloses a valve actuating means compromising a radially extending handle which is disposed about the valve stem and includes projections which engage the valve hand wheel or its spokes.
A similar construction is illustrated in U.S. Pat. No. 2,920,517 wherein an elongate handle is received on the stem of the valve and a pair of spaced apart projections straddle a valve spoke and engage the hand wheel.
U.S. Pat. Nos. 2,086,722 and 2,539,262 disclose valve turning tools which both engage only the outer wheel portion of the hand wheel at two spaced apart locations.
U.S. Pat. Nos. 2,682,189 and 4,715,252 both disclose wrench like valve tools which engage the handwheel at one location. While these tools as well as several of the foregoing facilitate the application of increased torque to the valve handwheel, they have in common a significant disadvantage. Because they apply unbalanced force to the handwheel at a single location, a static bending moment is created. Such unbalanced force application is less efficient than balanced, i.e., on center, torque application and can also damage the valve.
Study of the foregoing patented devices reveals another difficulty. Many of these devices may slip upon the valve handwheel when torque is applied. Clearly an abrupt, spontaneous repositioning of the device on the handwheel is undesirable. Furthermore, many of these designs are not self retaining and will disconnect and fall from the valve handwheel if not held in position by an operator. Finally, many of the foregoing devices are suitable for only a specific size or limited range of sizes of valve handwheels.
My prior U.S. Pat. No. 5,203,240 addresses many of these problems. Here, a circular drive member having a plurality of T-shaped slots engages the spokes of a valve handwheel and is rotated by a ratchet drive mechanism having a handle. While this device addresses many of the problems of the prior art, the opening and closing of a large valve which may require several turns and significant torque application through a ratchet mechanism can be tedious and time consuming.
The foregoing suggests that improvements to devices for applying torque to valve handwheels are both desirable and possible.